An ever-present concern in the manufacture of paper containers is to provide a rigid container which is capable of holding a substantial amount of fluid without collapsing when grasped by the consumer. It is also a major concern that such rigid containers be manufactured in an economical manner.
Paper container rigidity is defined by that load which when applied to the sidewalls of the container deflects the sidewall of the container inwardly one quarter of an inch. Further, this test is carried out at a point on the sidewall of the container which is two-thirds the height of the overall container. In defining the rigidity of a particular container, both dry as well as wet measurements are to be taken. Dry rigidity is measured using an empty container while wet rigidity measurements are taken at a predetermined time period, such as ten minutes after the cup has been filled with water. This rigidity test determines the ability of the container to be picked up by the consumer without collapsing inwardly and spilling the contents when the container is grasped on the sidewall.
The rigidity of a particular container is effected by the tensile and bending stiffness in both the vertical and circumferential directions of the container. One expedient for increasing the rigidity of a paper container is to form a brim about the top of the containers. As is disclosed in U.S. Pat. No. 2,473,836 issued to Vixen et al., conventional brim curling mechanism utilize complimentary curved dies in which the lower die is first moved upwardly around the upper end of the cup and to the top edge of the cup where it firmly holds the cup top against an upper die. The upper die is then moved downwardly to engage the uppermost edge of the cup between the dies with both of the dies then moving downwardly together to curl the upper edge of the container thereby forming a brim. This brim adds significantly to the rigidity of the overall cup structure.
Similarly, U.S. Pat. No. 3,065,677 issued to Loeser discloses a brim curling mechanism for containers. A lower die having a curve forming upper surface is maintained stationary while an upper die having a curve forming lower surface descends downwardly toward the stationary lower die, deflecting the upper edge portion of the cup secured by the lower die and again forming a brim about the upper periphery of the container. This brim, as stated previously, adds significantly to the overall rigidity of the container.
As is illustrated in FIG. 1A, each of the above-mentioned containers are formed with the machine direction of the paper material aligned in the axial direction of the container and the cross-machine direction of the paper material aligned in the circumferential direction of the container as shown by the arrows MD.sub.1 and CD.sub.1, respectively. Paper, when formed using conventional paper manufacturing processes has what is known in the art as a machine direction and a cross-machine direction. The machine direction of paper is generally that axis of the paper along which the paper moved as it was being formed. The cross-machine direction is perpendicular to the machine direction of the paper and has approximately twice the maximum stretch as that of the machine direction, while the tensile and bending stiffness of the board in the machine direction is greater than that in the cross-machine direction. Therefore, in order to easily form brims 4 about the upper periphery of the cup or container 2, the paper blank used in forming the cup 2 would be positioned as illustrated in FIG. 1A.
While the above-mentioned conventional paper containers are of the type having the machine direction of the paper material aligned with the vertical or axial direction of the resultant container, U.S. Pat. No. 2,473,840 issued to Amberg illustrates a paper container in the form of a conical paper cup being manufactured from a blank which is cut from a paper strip having a machine direction and a cross-machine direction. Accordingly, when the conical paper cup is formed, only a limited portion of the upper periphery of the conical paper cup will have the machine direction of the paper blank extending about the circumference of the cup. Additionally, a limited portion of the cross-machine direction of the paper blank extending in the circumferential direction of the conical paper cup will exist with the remaining and substantial portion of the upper periphery being somewhere between the machine direction and the cross-machine direction of the paper blank. Consequently, a brim or bead may be formed about the upper periphery of the conical paper cup using conventional die presses because the overall stretch of the paper about the upper periphery of the conical cup is greater than that of a cup having the entire upper periphery of the cup aligned substantially in the machine direction of the paper blank. Moreover, the rigidity of a conical cup formed in accordance with U.S. Pat. No. 2,473,840 will vary depending upon the particular point at which a rigidity test is applied. Therefore, the tensile and bending stiffness of the conical cup will vary significantly about the perimeter resulting in a non-uniform construction.
As is illustrated in U.S. Pat. No. 2,288,896 issued to Fink, containers having the machine direction of the paper material extending in the circumferential direction of the container have been manufactured. However, such containers are formed from a plurality of laminated layers and include metallic end closures. Containers formed in the above-mentioned manner are to be used for containing objects, such as blueprints, and, therefore, the significant drawbacks in forming brims or beads about an upper periphery of such containers is not of concern during the above-mentioned manufacturing process because such containers are not for the consumption of liquids by consumers.
In view of the foregoing, there is clearly a need for a container and more specifically a drinking cup formed of a paper material which exhibits a high degree of rigidity while having a brim or bead formed about an upper periphery thereof in order to add to the rigidity of the cup and to protect the consumer when the liquid contents of the cup are consumed.